TheGradient-Sensing Mechanism inBacterial Chemotaxis

A "temporalgradientapparatus" has beendeveloped thatallowsthemotility ofbacteria tobe studied after theyhavebeensubjected toasuddenchange fromoneuniformconcentration ofattractant toanother. A suddendecrease elicits thetumblingresponse observed withspatial gradients; itwasfound, however, thatasud- denincrease alsoelicits a response, namelysupercoordi- natedswimming.Thisdemonstrates thatchemotaxis is achieved bymodulation oftheincidence oftumblingboth aboveand belowitssteady-state value.The initial re- sponsesgradually reverttothesteady-state motility pat- terncharacteristic ofauniformdistribution ofattractant. Theapparentdetection ofa spatial gradient by thebac- teriatherefore involves anactualdetection ofatemporal gradient experienced asa resultofmovementthrough space.Potential modelsforthechemotactic response